1. Field of the Invention
The present invention relates generally to end dams and, more particularly, to an end dam for use on a waterbox of a paper making machine.
2. Description of the Prior Art
End dams have been described in the prior art. However, none of the prior art discloses the unique features of the present invention.
In U.S. Pat. No. 4,434,194, dated Feb. 28, 1984, Gerbert, et al., disclosed an edge dam assembly for an applicator for applying a film of coating material on a moving web of paper carried through an application zone, characterized by a seal element at each side end of the zone. To prevent leakage of coating liquid past the seal element, air is introduced through the element and into the side end of the zone adjacent to the element. The air forms an air barrier pocket at the side end of the zone, which is void of coating liquid, whereby coating liquid is maintained in the zone inwardly of the seal elements.
In U.S. Pat. No. 4,426,412, dated Jan. 17, 1984, Gebert, et al., disclosed an edge dam for an applicator for applying a film of coating liquid to a moving web of paper carried through an application zone, characterized by a seal element at each side end of the zone for substantially sealing the side end of the zone, thereby to impede a flow of coating material out of the zone. At least one orifice is formed through the seal element outwardly of the zone, and the orifice is connected with a supply of water under pressure for directing a flow of water against the peripheral edge of the web moving therepast, thereby to wet the edge and flush the same of any coating material seeping past the element. In consequence, edge tickers and coating liquid pickup on the web edge are substantially eliminated.
In U.S. Pat. No. 4,358,481, dated Nov. 9, 1982, Wallsten disclosed a method and apparatus for coating both sides of a moving web, such as a paper web, with the same coating material on both sides by feeding the web downwardly between a rotating support roller and a coating blade directed against said roller. One side of the web is partially wrapped around said roller and a first excess of coating material intended for the web side facing said roller is applied to the roller before or at the point of contact between said web and the roller. A second excess of coating material is applied to the other side of the web by feeding the web through a dam of coating material arranged below said contact point--in the moving direction of the web--said dam being formed substantially between said coating blade and holder and the said other side of the web. The excess coating material is laterally expressed in said dam beneath the top level thereof.
In U.S. Pat. No. 4,706,603, dated Nov. 17, 1987, Wohlfeil disclosed a coating apparatus for fabric webs carried along a counter roll including an applicator which accommodates a chamber containing coating color to be applied onto the fabric web. The chamber is defined by spaced doctor blade and overflow plate and dam elements laterally sealing the chamber. For preventing a coating of the web along its edges, separate doctor assemblies are provided which are controlled independently of the dam plates.
In U.S. Pat. No. 4,259,921, dated Apr. 7, 1981, Wallsten disclosed an apparatus selectively convertible to perform one or more coating operations on a web of paper or the like comprising a fixed rotatable roller, a coating blade movable into and out of coating relation with the surface of the fixed roller and cooperating with a dam of coating material to coat a web as it passes through the nip between the coating blade and the fixed roller, and a second movable roller movable into and out of nip forming relation with the fixed roller with provision for adjustment of pressure in the nip and adapted to cooperate with a dam of coating material to coat a web as it passes through the nip between said rollers, said movable roller also being adapted alternatively to receive coating material and to transfer it to the fixed roller to coat one side of a web as it runs over the latter.
In U.S. Pat. No. 5,795,393, dated Aug. 18, 1998, Isfort disclosed a coating edge limiter for a coating arrangement with a short dwell time. Color is fed under pressure into a coating chamber formed by a backing roll around which a paper web is guided, a barrier wall, a doctor blade element and sealing blocks located at both ends of the coater. A formatting plate almost completely covers an application zone between the doctor blade element and the barrier wall so that an edge region of the web is sharply delineated and kept completely free of color. In each of the sealing blocks water is supplied via channels to depressions thereby forming a pressure cushion. This pressure cushion prevents the pressurized color to the coating chamber from flowing out laterally and ensures that the formatting plate is pressed flatly against the web. The coating edge limiter thereby makes it possible to establish very precisely the width of the web to be produced.
In U.S. Pat. No. 4,503,804, dated Mar. 12, 1985, Damrau disclosed an improved edge seal assembly for an applicator for applying a coating liquid to a moving web of paper, wherein the applicator is of the type having a chamber for receiving the coating liquid and an elongate opening thereto for directing the liquid onto the web, the opening being formed between a front wall of the chamber and a doctor blade extending from the rear side of the opening to against the web, characterized by a seal element sealed with the front wall and doctor blade in an end space therebetween, and a deckle beneath the seal element for closing off a selected portion of the side end of the opening. The seal element and the deckle are slidingly interconnected and can be independently adjusted laterally with respect to the opening.
In U.S. Pat. No. 4,327,662, dated May 4, 1982, Damrau disclosed an improved edge or end dam assembly for an applicator for applying a coating liquid to a web of moving paper carried on a backing roll, the applicator being of the type having a chamber for receiving the coating liquid and an opening therein for directing the liquid onto the web, the opening being formed between a front wall of the chamber and a doctor blade, extending from the rear of the opening to against the web, characterized by a seal element sealed with the front wall and doctor blade in an end space therebetween and extending toward and closely adjacent but spaced from the web. The face of the seal element adjacent the paper web has a plurality of grooves extending generally parallel to the direction of movement of the web, so that coating material which seeps past the seal element and beyond the edge dam assembly enters the grooves and is moved by the web toward the doctor blade for deposit on the web. In this manner, leakage of coating material past the seal element is significantly minimized, and pressure of coating material on the web may be maintained.
In U.S. Pat. No. 4,354,452, dated Oct. 19, 1982, Patterson disclosed an edge dam or edge seal assembly for an applicator for applying a coating liquid to a moving web of paper carried on a backing roll, the applicator being of the type having a chamber for receiving coating liquid and an opening therein for directing the liquid onto the web, the opening being formed between a front wall of the chamber and a doctor blade extending from the rear of the opening to against the web, characterized by an expandable seal element sealed with the front wall and doctor blade in an end space therebetween and extending toward and closely adjacent to but spaced from the web. The seal element is of a flexible material and accommodates the introduction of pneumatic or hydraulic fluid under pressure therein for expanding the same to a size which fits the end space and seals the same, and which extends a sealing surface of the element very closely adjacent to the web or backing roll. Consequently, leakage of coating past the seal element may be accurately controlled and significantly minimized.
While these end dams may be suitable for the purposes for which they were designed, they would not be as suitable for the purposes of the present invention, as hereinafter described.